Micro-channel heat exchanger

ABSTRACT

A heat exchanger comprising a process tube attached in heat conducting contact with a hydronic tube. The process tube has a plurality of hydraulically discrete internal passageways that extend through the process tube. The hydronic tube has at least one passageway that extends through the hydronic tube. Optionally, the process tube can be sandwiched between a pair of hydronic tubes so that two heat transfer surfaces on the process tube are in heat conducting contact with heat transfer surfaces on each of the hydronic tubes. Also optionally, the heat exchanger can include a plurality of process tubes that are sandwiched between a plurality of hydronic tubes with each process tube being disposed between a pair of hydronic tubes. The attached tubes can be shaped into a variety of configurations depending on the application in which the heat exchanger will be used.

FIELD OF THE INVENTION

[0001] The present invention relates to heat exchangers and, more particularly, to heat exchangers made from flattened tubes that are sandwiched together and shaped into a variety of configurations.

BACKGROUND OF THE INVENTION

[0002] Typical heat exchangers for use as either evaporators or condensers come in a variety of configurations. A typical heat exchanger has a tube with an internal passage that allows a fluid to flow therethrough. The tube can be configured into a variety of orientations, such as sinuous or serpentine, coiled, etc. The tube may be in heat conducting contact with a second tube that also has an internal passageway that allows a different fluid to flow therethrough. Alternatively, the tube may have heat conducting fins attached along an exterior of the tube to facilitate heat transfer.

[0003] The dominant mode of heat transfer in the tube is through conduction. When two-phase flow is occurring in the passageway, the liquid component of the two-phase flow will conductively transfer heat through the portion of the tube that is in contact with the liquid while the gas component will convectively transfer heat. Because the heat transfer rate in conduction is much greater than that of convection, it would be desirable to provide a heat exchanger design that maximizes the conductive heat transfer properties of the heat exchanger during two-phase flow.

[0004] The passageways in the tubes are typically dimensioned such that gravity will play a dominant role on the location of a liquid component in a two-phase flow passing through the tube. That is, the liquid portion of the two-phase flow would be concentrated along the lower portions of the horizontal sections of the tube. Because the liquid portion is concentrated in only a portion of the passageways, the entire passageway is not used efficiently to obtain the most effective heat transfer (i.e. conductive heat transfer). That is, if the liquid layer were to encompass the entire periphery of the passageway, the heat transfer would be much greater and the efficiency of the heat exchanger would increase. The increased efficiency would allow the heat exchanger to be reduced in size and cost. Therefore, it would be desirable to provide a heat exchanger design that allows for more efficient heat transfer in a two-phase flow.

SUMMARY OF THE INVENTION

[0005] A heat exchanger according to the principles of the present invention provides an increased heat transfer rate. The increased heat transfer rate allows the heat exchanger to be smaller in size and reduces the cost.

[0006] A heat exchanger according to the principles of the present invention comprises first and second flattened tubes. Each tube has first and second ends with an intermediate portion therebetween and opposite heat transfer surfaces that extend between the first and second ends. The first tube has a plurality of hydraulically discrete internal passageways that extend through the first tube between the first and second ends and allows a fluid to pass therethrough. The second tube has at least one internal passageway that extends through the second tube between the first and second ends and allows a fluid to pass therethrough. The second tube is disposed adjacent the first tube with the intermediate portions abutting and portions of the heat transfer surfaces that extend along the intermediate portions being in heat conducting contact. A first pair of manifolds is attached to and in fluid communication with the first and second ends of the first tube so that a fluid can pass between the first pair via the plurality of passageways in the first tube. A second pair of manifolds is attached to and in fluid communication with the first and second ends of the second tube so that a fluid can pass between the second pair via the at least one passageway in the second tube.

[0007] A method of making a heat exchanger according to the principles of the present invention is also disclosed. The method includes the steps of: 1) attaching an intermediate portion of a first flattened tube to an intermediate portion of a second flattened tube so that the intermediate portions are abutting and portions of heat transfer surfaces on the first and second tubes are in heat conductive contact; 2) attaching a first pair of manifolds to ends of the first tube so that each manifold of the first pair is attached to different ends of the first tube; 3) attaching a second pair of manifolds to ends of the second tube so that each manifold of the second pair is attached to different ends of the second tube; and 4) shaping the attached tubes into a predetermined configuration.

[0008] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0010]FIG. 1 is a perspective view of a heat exchanger according to the principles of the present invention;

[0011]FIG. 2 is a partial cross-sectional view of the tubes of the heat exchanger of FIG. 1 along line 2-2;

[0012] FIGS. 3A-D are side plane views of various configurations for the heat exchanger of FIG. 1;

[0013] FIGS. 4A-B are perspective views of different heat exchangers according to the principles of the present invention;

[0014]FIG. 5 is a partial cross-sectional view of the heat exchangers shown in FIGS. 4A-B along line 5-5;

[0015] FIGS. 6A-D are side plan views of various configurations for the heat exchangers of FIGS. 4A-B;

[0016]FIG. 7 is a perspective view of a different heat exchanger according to the principles of the present invention;

[0017]FIG. 8 is a partial cross-sectional view of the heat exchanger of FIG. 7 along line 8-8;

[0018] FIGS. 9A-D are side plan views of various configurations for the heat exchanger of FIG. 7; and

[0019]FIG. 10 is a perspective view of a manifold that can be used with the heat exchangers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0021] Referring to FIG. 1, there is shown a heat exchanger 20 in accordance with the principles of the present invention. The heat exchanger 20 is comprised of a process tube 22 abutting a hydronic tube 24. The process tube 22 has first and second end portions 26, 28 and an intermediate portion 30 therebetween. The process tube 22 also has opposite first and second heat transfer surfaces 32, 34. The first and second heat transfer surfaces 32, 34 of the process tube 22 are the primary heat transfer surfaces and have significantly more surface area than the sides 35 of the process tube 22. The process tube 22 has a plurality of internal passageways 36 that extend from the first end portion 26 through the process tube 22 to the second end portion 28. Each of the passageways 36 is hydraulically discrete. The passageways 36 allow a fluid to pass through the process tube 22 from the first end portion 26 to the second end portion 28. The first and second end portions 26, 28 of the process tube 22 are attached in fluid communication to respective first and second manifolds 37, 38. Preferably, the first and second manifolds 37, 38, as shown in FIG. 10, each have a slot 39 that is configured to receive one of the end portions 26, 28 of the process tube 22. That is, the first end portion 26 is inserted into a slot 39 in the first manifold 37 and the second end portion 28 is inserted into a slot 39 in the second manifold 38. The manifolds 37, 38 each have a passageway 40 that is in fluid communication with the passageways 36 in the process tube 22. A process fluid can then pass from the first manifold 37 through the process tube 22 and into the second manifold 38 via the passageways 36. The first and second end portions 26, 28 can be attached to the respective first and second manifolds 37, 38 by a variety of ways, as will be apparent to those skilled in the art. For example, the manifolds 37, 38 can be attached to the end portions 26, 28 with an adhesive or by brazing.

[0022] The hydronic tube 24 has first and second end portions 41, 42 and an intermediate portion 44 that extends therebetween. The hydronic tube 24 has opposite first and second heat transfer surfaces 46, 48. The first and second heat transfer surfaces 46, 48 are the primary heat transfer surfaces and have significantly more surface area than sides 50 of the hydronic tube 24. The hydronic tube 24 has at least one internal passageway 52 that extends from the first end portion 41 through the hydronic tube 24 to the second end portion 42. The at least one passageway 52 allows a fluid to pass through the hydronic tube 24 from the first end portion 41 to the second end portion 42. The first and second end portions 41, 42 of the hydronic tube 24 are attached in fluid communication to respective first and second manifolds 54, 56. Preferably, the first and second manifolds 54, 56, as shown in FIG. 10, each have a slot 39 that is configured to receive one of the end portions 41, 42 of the hydronic tube 24. That is, the first end portion 41 is inserted into a slot 39 in the first manifold 54 and the second end portion 42 is inserted into a slot 39 in the second manifold 56. The manifolds 54, 56 each have a passageway 60 that is in fluid communication with the at least one passageway 52 in the hydronic tube 24. A hydronic fluid can then pass from the first manifold 54 through the hydronic tube 24 and into the second manifold 56 via the at least one passageway 52. The first and second end portions 41, 42 can be attached to the respective first and second manifolds 54, 56 by a variety of ways, as will be apparent to those skilled in the art. For example, the manifolds 54, 56 can be attached to the end portions 41, 42 with an adhesive or by brazing.

[0023] The process tube 22 and the hydronic tube 24 are disposed adjacent one another with the intermediate portions 30, 44 abutting. The abutment of the intermediate portions 30, 44 causes one of the heat transfer surfaces 32, 34 of the process tube 22 to be in heat conducting contact with one of the heat transfer surfaces 46, 48 of the hydronic tube 24. For example, as can be seen in FIG. 2, the second heat transfer surface 34 of the process tube 22 is in heat conducting contact with the first heat transfer surface 46 of the hydronic tube 24. Preferably, the intermediate portions 30, 44 are attached together. Intermediate portions 30, 44 can be attached in a variety of ways, as will be apparent to those skilled in the art. For example, the intermediate portions 30, 44 can be attached with an adhesive or by brazing.

[0024] The attachment of the process tube 22 to the hydronic tube 24 allows the tubes 22, 24 to be shaped into a variety of configurations depending upon the application in which the heat exchanger 20 is to be used. That is, the intermediate portions 30, 44 can be shaped into a variety of configurations to fit within the application in which the heat exchanger 20 is to be employed. For example, as shown in FIG. 1, the intermediate portions 30, 44 can extend in a generally straight configuration. In other applications, the intermediate portions 30, 44 may not be generally straight. For example, as shown in FIGS. 3A-D, the intermediate portions 30, 44 can take a variety of shapes or configurations. As shown in FIG. 3A, the intermediate portions 30, 44 can have a single 90 degree bend and have a general L-shaped configuration. As shown, in FIG. 3B, the intermediate portions 30, 44 can have a pair of generally 90 degree bends and be configured into a generally U-shaped heat exchanger 20. As can be seen in FIG. 3C, the intermediate portions 30, 44 can extend sinuously between the respective end portions 26, 28, 41, 42. The heat exchanger 20, as can be seen in FIG. 3D, can also be configured so that the intermediate portions 30, 44 are coiled. It should be understood that the various configurations shown in the Figures and discussed above for the heat exchanger 20, are exemplary in nature and that the intermediate portions 30, 44 can be configured into different shapes, as will be apparent to those skilled in the art, and still be within the scope of the invention as defined by the claims.

[0025] As can be seen in FIG. 2, the passageways 36 in the process tube 22 each have a peripheral wall 62 that defines a periphery of each passageway 36. The peripheral walls 62 are comprised of upper and lower portions 66, 68 and side portions 70. The upper portions 66 are adjacent the first heat transfer surface 32 and the lower portions 68 are adjacent the second heat transfer surface 34. The side portions 70 separate the passageways 36 from one another and also serve as the sides 35 of the process tube 22. The passageways 36 can come in a variety of configurations. For example, as shown in FIG. 2, the passageways 36 can be rectangular shaped and/or D-shaped. Other configurations of the passageways 36, as will be apparent to those skilled in the art, can be employed without departing from the scope of the invention as defined by the claims.

[0026] Preferably, as shown in FIG. 2, the at least one passageway 52 in the hydronic tube 24 is one of a plurality of passageways 52. The passageways 52 in the hydronic tube 24 each have a peripheral wall 71 that defines a periphery of each passageway 52. The peripheral walls 71 are comprised of upper portions 72, lower portions 74 and side portions 76. The upper portions 72 are adjacent the first heat transfer surface 46 while the lower portions 74 are adjacent the second heat transfer surface 48. The side portions 76 separate adjacent passageways 52 from one another along with serving as the sides 50 of the hydronic tube 24. The passageways 52 can come in a variety of configurations. For example, as shown in FIG. 2, the passageways 52 can be rectangular shaped and/or D-shaped. Other configurations of the passageways 52, as will be apparent to those skilled in the art, can be employed without departing from the scope of the invention as defined by the claims.

[0027] The heat exchanger 20 formed by the process tube 22 and the hydronic tube 24 is used to exchange heat between a process fluid that is flowing through the passageways 36 in the process tube 22 and a hydronic fluid that is flowing through the passageways 52 in the hydronic tube 24. The transfer of heat occurs through a variety of mechanisms, as is known in the art. One mechanism of heat transfer is that of conductive heat transfer. The term conduction refers to the heat transfer that will occur across stationary mediums, which may be a solid or a fluid. Conduction will occur throughout each of the tubes 22, 24. The primary conductive heat transfer between the process fluid and the hydronic fluid occurs through the abutting heat transfer surfaces 34, 46 of the tubes 22, 24 and through the peripheral walls 62, 71 that define the passageways 36, 52 in the respective process and hydronic tubes 22, 24. A second mode of heat transfer that occurs is that of convection. The term convection refers to heat transfer that will occur between a surface and a moving fluid when they are at different temperatures. Convection occurs between the process fluid flowing through the passageways 36, the boundary layer of process fluid on the peripheral walls 62 and/or the peripheral walls 62 that define the passageways 36. Convection also occurs between the hydronic fluid flowing through the passageways 52, the boundary layer of hydronic fluid on the peripheral walls 71 and/or the peripheral walls 71 that define the passageways 52.

[0028] According to Fourier's law of conduction, the rate at which energy is transferred is proportional to the thermal conductivity of the material. Fourier's law of conduction for one dimensional flow in steady state conditions can be represented by the equation q″_(x)=−KΔT/L; where q″_(x) is the rate of heat transfer in the x direction, K is the thermal conductivity, ΔT is the temperature difference, and L is the distance through which the heat is transferred. A material having a high thermal conductivity, typically 100 W/m·K or higher, will result in little resistance to heat transfer. Preferably, the process and hydronic tubes 22, 24 are made from a material that has a relatively high thermal conductivity, as is known in the art. For example, the process and hydronic tubes 22, 24 can be made from aluminum, copper or a variety of other materials, as will be apparent to those skilled in the art, to provide process and hydronic tubes 22, 24 that have a high thermal conductivity. The high thermal conductivity of the process and hydronic tubes 22, 24 results in little resistance to conductive heat transfer and is not a limiting factor in the transfer of heat between the hydronic and process fluids. The main resistance that occurs to the transfer of heat between the hydronic and process fluids is that of the convective process inside the passageways 36 in the process tube 22 and the passageways 52 in the hydronic tube 24. Because the convective heat transfer process is a limiting factor for the heat transfer between the hydronic and process fluids, it is desirable to increase the role of conductive heat transfer and/or decrease the role and/or resistance of convective heat transfer to thereby increase the heat transfer that will occur between the process and hydronic fluids.

[0029] Convective resistance to heat transfer is inversely proportional to the heat transfer coefficient. By the definition of the Nusselt number (defined as the ratio of the total heat transfer to the convective heat transfer), the heat transfer coefficient is inversely proportional to the diameters of the passageways through which the fluid flows. Hence, a smaller diameter passageway 36 in the process tube 22 and/or a smaller diameter passageway 52 in the hydronic tube 24 results in a higher heat transfer coefficient. The higher heat transfer coefficient results in a lower resistance to the convective heat transfer process between the process and hydronic fluids. Thus, smaller passageways 36 in the process tube 22 and/or smaller passageways 52 in the hydronic tube 24 enhance the heat exchange process and allow for more energy to be exchanged between the process and hydronic fluids. Preferably, the passageways 36, 52 are dimensioned to increase the heat transfer coefficient and enhance the heat transfer of the heat exchanger 20, as will be discussed in more detail below. The small size of the passageways 36, 52 provides a significant advantage over prior art heat exchangers that typically use much larger passageway sizes and are limited by the large convective heat transfer resistances associated with those larger size passageways.

[0030] The heat transfer that occurs between the process and hydronic fluids is also dependent upon the flow regime that occurs within the passageways 36, 52. When the heat exchanger 20 is used as an evaporator, the process fluid would be a two-phase flow of a liquid and gas. The hydronic fluid flowing through the hydronic tube 24 would typically be a liquid, although a two-phase phase flow of liquid and gas may also occur in the hydronic tube 24. For purposes of explaining the invention, the hydronic fluid flowing through the hydronic tube 24 will be assumed to be a liquid and not a two-phase flow. However, it is to be understood that when the hydronic fluid is a two-phase flow, the principles of the invention that are directed to and enhance heat transfer related to the process fluid being a two-phase flow, are equally applicable to the hydronic fluid and can be applied to the construction of the hydronic tube 24.

[0031] The particular flow regime established by a given combination of liquid and gas-phase velocities within the passageways 36 depend upon the interaction of gravity, shear (inertia) and surface tension forces. The flow mechanisms in small diameter round and rectangular passageways are different from those in larger diameter passageways primarily due to the different relative magnitudes of these forces. In tubes having passageways with hydraulic diameters less than 2.5 millimeters (small hydraulic diameters), surface tension forces dominate and gravity forces on the liquid become negligible. The hydraulic diameter is defined as four times the cross sectional area of the passageway divided by the wetted perimeter of the passageway. In the small hydraulic diameters, preferred flow patterns such as intermittent or annular flow dominate the flow process. These flow regimes will occur in both horizontal and vertical orientations. In both of these forms of flow, the two-phase mixture exhibits a configuration such that the liquid exists as a circumferential film and the gas exists in the form of a Taylor bubble or as a gas core. Hence, in these smaller hydraulic diameters, liquid is pulled up against gravity by the surface tension forces around the circumference of the passageway peripheral wall 62. This is contrary to the larger hydraulic diameter passageways or tubes where stratification of the liquid and gas occurs—and a significantly larger resistance to evaporative heat transfer exists on the top of the passageway wall which can render nearly 50 percent of the passageway inoperable during the heat exchange process. However, in the smaller hydraulic diameter passageways, the internal resistance to heat transfer is equally distributed around the entire passageway wall 62—thus allowing both the top and bottom of the passageway 36 to be used during the heat exchange process. This is true for both horizontal and vertical applications.

[0032] Therefore, the smaller hydraulic diameter passageways result in a uniform distribution of heat transfer resistance and increases the amount of heat transfer that occurs between the hydronic and process fluids as a result of the convective and conductive process. The increased heat transfer increases the overall efficiency of a heat exchanger utilizing passageways having the smaller hydraulic diameters. The increased heat transfer capacity and efficiency enables a heat exchanger for use in a given application to be smaller when the heat exchanger utilizes passageways that have the smaller hydraulic diameters.

[0033] Preferably, the heat exchanger 20 has a process tube 22 that has passageways 36 that are of the smaller hydraulic diameter type. Preferably, the passageways 36 in the process tube 22 have a hydraulic diameter that is less than 2.5 millimeters. It is even more preferred that the passageways 36 each have hydraulic diameters of less than approximately 2.0 millimeters. It is still even more preferable, that each passageway 36 have a hydraulic diameter of less than approximately 1.5 millimeters. When the hydronic fluid flowing through the hydronic tube 24 is also a two-phase flow, it is preferred that the passageways 52 each have a hydraulic diameter of less than 2.5 millimeters. Even more preferably, the passageways 52 each have a hydraulic diameter of less than approximately 2.0 millimeters. Still even more preferably, the hydraulic diameter of each of the passageways 52 is less than approximately 1.5 millimeters. It should be understood that each passageway 36 in the process tube 22 does not need to have an identical hydraulic diameter. That is, each passageway 36 in the process tube 22 can have a different hydraulic diameter and still be within the scope of the invention. Likewise, each of the passageways 52 and the hydronic tube 24 also do not need to have an identical hydraulic diameter and the hydraulic diameters can vary and still be within the scope of the invention as defined by the claims.

[0034] As can be seen in FIG. 2, the exchange of heat between the hydronic fluid and the process fluid will occur convectively in the passageways 36, 52 and conductively through the tubes 22, 24 via the attached heat transfer surfaces 34, 46. Because the passageways 36 in the process tube 22 are of the smaller hydraulic diameter type, as was discussed above, the liquid portion of the process fluid in the process tube 22 will extend along the upper, lower and side portions 66, 68, 70 of the peripheral walls 62, regardless of the orientation, and allow heat transfer to occur along the entire periphery of the peripheral walls 62. Because the conduction heat transfer is still substantially larger than the convective heat transfer, even with the small hydraulic diameters of the passageways 36, the heat transferred from the upper and side portions 66, 70 of the peripheral walls 62 will be conductively transferred through the process tube 22 via the second heat transfer surface 34 and sides 35 to the first heat transfer surface 46 of the hydronic tube 24. The heat transfer will then travel to the first heat transfer surface 46 of the hydronic tube 24 and on to the hydronic fluid via the upper, lower and side portions 72, 74, 76 of the peripheral walls 71 of the passageways 52. That is, because the conductive heat transfer is still significantly larger than the convective heat transfer, the fact that the first heat transfer surface 32 of the process tube 22 is not in direct heat conducting contact with a heat transfer surface of the hydronic tube 24, the benefit provided by the increased heat transfer due to the use of smaller hydraulic diameter passageways 36 still increases the overall efficiency of the heat exchanger 20. Thus, it is not required that both heat transfer surfaces 32, 34 of a process tube 22 be in heat conducting contact with heat transfer surfaces 46, 48 on a hydronic tube 24 to realize the benefit associated with the use of smaller hydraulic diameter passageways 36.

[0035] While it is not necessary for both the first and second heat transfer surfaces 32, 34 of the process tube 22 to be in heat conducting contact with heat transfer surfaces on the hydronic tube 24 to enjoy the enhanced heat transfer efficiency associated with the use of smaller hydraulic diameter passageways 36, the process tube 22 can be sandwiched between a pair of hydronic tubes 24 to form another heat exchanger according to the principles of the present invention. That is, as can be seen in FIGS. 4A and 4B, a heat exchanger 20′ can have a process tube 22′ disposed between a pair of hydronic tubes 24′. The intermediate portions 30′ of the process tube 22′ are abutting the intermediate portions 44′ of the hydronic tubes 24′ so that the heat transfer surfaces 32′, 34′ of the process tube 22′ are in heat conducting contact with the heat transfer surfaces 48′, 46′ on the hydronic tubes 24′. That is, as can be seen in FIG. 5, the first heat transfer surface 32′ of the process tube 22′ is in heat conducting contact with the second heat transfer surface 48′ of the upper hydronic tube 24′ and the second heat transfer surface 34′ of the process tube 22′ is in heat conducting contact with the first heat transfer surface 46′ of the lower hydronic tube 24′. The heat transfer surfaces 32′, 34′ of the process tube 22′ thereby being sandwiched between heat transfer surfaces of a pair of hydronic tubes 24′. The sandwiching of the process tube 22′ between a pair of hydronic tubes 24′ allows for another path of heat transfer to occur between hydronic fluids in the hydronic tubes 24′ and the process fluid in the process tube 22′. That is, heat can be transferred conductively and convectively between the process fluid in the process tube 22′ and a hydronic fluid in the upper hydronic tube 24′ and the hydronic fluid and the lower hydronic tube 24′. The additional path for heat transfer enables even more efficient operation of heat exchanger 20′ having the process tube 22′ sandwiched between a pair of hydronic tubes 24′.

[0036] Preferably, as can be seen in FIG. 5, the passageways 36′ in the process tube 22′ are similar to the passageways 36 shown in FIG. 2. Likewise, it is preferred that the passageways 52′ in each of the hydronic tubes 24′ is also similar to the passageways 52 shown in FIG. 2. That is, it is preferred that each passageway 36′ in the process tube 22′ have a smaller hydraulic diameter such that the process fluid would form a liquid layer that extends around the entire peripheral wall 62′ of each passageway 36′. Likewise, it is preferred that each passageway 52′ in the hydronic tubes 24′ also have the smaller hydraulic diameter so that when the hydronic fluid is a two-phase flow, a liquid layer of hydronic fluid extends along the entire peripheral wall 71′ of each passageway 52′. The heat exchanger 20′ thereby is more efficient due to the increased heat transfer associated with the smaller hydraulic diameter passageways 36′, 52′.

[0037] As can be seen in FIGS. 4A and 4B, when the process tube 22′ is sandwiched between a pair of hydronic tubes 24′, the end portions 26′, 28′ of the process tube 22′ and the end portions 41′, 42′ of the pair of hydronic tubes 24′ can vary. For example, as shown in FIG. 4A, the first end portion 26′ of the process tube 22′ and the first end portions 41′ of the pair of hydronic tubes 24′ can diverge from one another as they extend from the respective intermediate portions 30′, 44′. Likewise, the second end portion 28′ of the process tube 22′ and the second end portions 42′ of the pair of hydronic tubes 24′ can also diverge as they extend from the respective intermediate portions 30′, 44′. When the end portions diverge, the heat exchanger 20′ utilizes more manifolds than was the case when the single process tube 22 was attached to a single hydronic tube 24 to form heat exchanger 20. That is, each hydronic tube 24′ of the pair of hydronic tubes 24′ will have a separate pair of manifolds that communicate with the passageways 52′ in the hydronic tube 24′. Therefore, as shown in FIG. 4A, the end portions 41′, 42′ of the upper hydronic tube 24′ are connected to the first and second manifolds 54′, 56′ while the first and second end portions 41′, 42′ of the lower hydronic tube 24′ are connected to third and fourth manifolds 78′ , 80′.

[0038] In a different embodiment of heat exchanger 20′, as shown in FIG. 4B, the first and second end portions 26′, 28′ of the process tube 22′ are generally aligned with and disposed between the first and second end portions 41′, 42′ of the pair of hydronic tubes 24′. The first and second end portions 41′, 42′ of the pair of hydronic tubes 24′ extend from the intermediate portions 44′ around the first and second manifolds 37′, 38′ that are attached to the respective first and second end portions 26′, 28′ of the process tube 22′ so that the first and second manifolds 37′, 38′ are disposed between the pair of hydronic tubes 24′. In this configuration, the pair of hydronic tubes 24′ share the same first and second manifolds 54′, 56′.

[0039] As can be seen in FIGS. 6A-D, the heat exchanger 20′ can be shaped into a variety of configurations, depending upon the application in which the heat exchanger 20′ is to be used. That is, the intermediate portions 30′, 44′ can be configured into a generally L-shaped configuration, as shown in FIG. 6A, a generally U-shaped configuration, as shown in FIG. 6B, a sinuous configuration, as shown in FIG. 6C, and a coiled configuration as shown in FIG. 6D. It should be understood that other configurations, as will be apparent to those skilled in the art, can also be employed without departing from the scope of the invention as defined by the claims.

[0040] In yet another aspect of the present invention, as can be seen in FIG. 7, a heat exchanger 20″ can have a plurality of process tubes 22″ each sandwiched between a plurality of hydronic tubes 24″. That is, as can be seen in FIG. 8, the heat exchanger 20″ has each process tube 22″ of the plurality of process tubes 22″ sandwiched between a pair of hydronic tubes 24″ of the plurality of hydronic tubes 24″. The cross-section of the heat exchanger 20″, as shown in FIG. 8, consists of alternating hydronic tubes 24″ and process tubes 22″. Preferably, there is one more hydronic tube 24″ than there are process tubes 22″ so that each process tube 22″ can be sandwiched between a pair of hydronic tubes 24″.

[0041] Preferably, as can be seen in FIG. 8, the passageways 36″ in each of the process tubes 22″ are similar to the passageways 36 shown in FIG. 2. Likewise, it is preferred that the passageways 52″ in each of the hydronic tubes 24″ are also similar to that shown in FIG. 2. That is, it is preferred that each passageway 36″ in the plurality of process tubes 22″ has a small hydraulic diameter such that the two-phase process fluid will form a liquid layer that extends around the entire peripheral wall 62″ of each passageway 36″. Likewise, it is preferred that each passageway 52″ in the plurality of hydronic tubes 24″ also has a small hydraulic diameter so that when the hydronic fluid is a two-phase flow, a liquid layer of hydronic fluid exists along the entire peripheral wall 71″ of each passageway 52″. The heat exchanger 20″ thereby is more efficient due to the increased heat transfer associated with the smaller hydraulic diameter passageways 36″, 52″.

[0042] When the heat exchanger 20″ has a plurality of process tubes 22″ that are each sandwiched between a pair of hydronic tubes 24″, as shown in FIG. 7, the respective end portions 26″, 28″, 41″, 42″ can take the configuration shown and will utilize a plurality of manifolds so that a process fluid can flow through the process tubes 22″ and a hydronic fluid can flow through the hydronic tubes 24″. That is, the first and second end portions 41″, 42″ of the central hydronic tube 24″ are attached to the respective first and second manifolds 54″, 56″ which are sandwiched between a pair of process tubes 22″, the first and second end portions 26″, 28″ of the process tubes 22″ are attached to the respective first and second manifolds 37″, 38″ which are sandwiched between an outer pair of hydronic tubes 24″, and the first and second end portions 41″, 42″ of the outer pair of hydronic tubes 24″ are attached to the respective third and fourth manifolds 78″, 80″. While the end portions 26″, 28″, 41″, 42″ are preferably configured as shown, it should be understood that other configurations for the end portions 26″, 28″, 41″, 42″ can be utilized, as will be apparent to those skilled in the art, without departing from the scope of the invention as defined by the claims.

[0043] The heat exchanger 20″ shown in FIG. 7 can be configured into a variety of shapes depending upon the application in which the heat exchanger 20″ is to be employed. For example, the intermediate portions 30″, 44″ can be configured, as shown in FIG. 9A, to be generally L-shaped, or, as shown in FIG. 9B, can be configured to be generally U-shaped, or, as shown in FIG. 9C, can be configured into a sinuous or serpentine shape, or, as shown in FIG. 9D, can be configured into a coil shape. While the heat exchanger 20″ has been shown as being capable of being configured into the variety of shapes shown in FIGS. 9A-D, it should be understood that other configurations, as will be apparent to those skilled in the art, can be employed without departing from the scope of the invention as defined by the claims.

[0044] The making of heat exchanger 20, 20′, 20″ according to the principles of the present invention will now be discussed. For convenience, the discussion of making the heat exchangers according to the principles of the present invention is going to be limited to reference to heat exchanger 20 shown in FIGS. 1-3D. When it is necessary to refer to the heat exchangers 20′, 20″ shown in FIGS. 4A-9D, the reference indicia will change accordingly. The heat exchanger 20 is made from a pair of flattened tubes 22, 24. While the tubes 22, 24 have been and will continue to be described as flattened tubes, it should be understood the term flattened tube should not be construed as being limited to a round tube that has been “flattened”, but rather, the term flattened tube should be construed to include tubing used in a heat exchanger that has opposite heat transfer surfaces along with at least one passageway that extends through the tube so that fluid can pass through the tube. The flattened tubes 22, 24 can be provided in a variety of ways, as is known in the art. For example, the tubes 22, 24 can be extruded.

[0045] The tubes 22, 24 are connected together by attaching an intermediate portion 30 of the process tube 22 to an intermediate portion 44 of a hydronic tube 24 so that the intermediate portions 30, 44 abut one another and portions of the second heat transfer surface 34 of the process tube 22 is in heat conducting contact with a portion of the first heat transfer surface 46 of the hydronic tube 24. The heat conducting contact between the second heat transfer surface 34 of the process tube 22 and the first heat transfer surface 46 of the hydronic tube 24 enables heat to be conductively transferred between the tubes 22, 24. First and second manifolds 37, 38 are then attached to the respective first and second end portions 26, 28 of the process tube 22 and first and second manifolds 54, 56 are attached to the respective first and second end portions 41, 42 of the hydronic tube 24. Alternatively, the manifolds can be attached to the tubes prior to attaching the intermediate portions. The end portions 26, 28, 41, 42 can be attached to the manifolds 37, 38, 54, 56 by inserting the end portions into a slot 39, 58, as shown in FIG. 10, in a manifold. The manifolds can be brazed to the end portions or can be attached with an adhesive, as is known in the art. After the process tubes 22, 24 are attached together and the manifolds are attached to the tubes 22, 24, the tubes 22, 24 can be shaped into a predetermined configuration, as is known in the art. For example, the attached tubes 22, 24 can be shaped by bending the tubes 22, 24 until the desired shape is attained.

[0046] When it is desired to make heat exchanger 20′a process tube 22′ is disposed between a pair of hydronic tubes 24′ with the intermediate portions 30′, 44′ abutting. The abutment of the intermediate portions 30′, 44′ causes the first and second heat transfer surface 32′, 34′ to be in heat conducting contact with the respective second and first heat transfer surfaces 48′, 46′ of the pair of hydronic tubes 24′. Optionally, the first and second manifolds 37′, 38′ can be attached to the respective first and second end portions 26′, 28′ of the process tube 22′ so that the first and second manifolds 37′, 38′ are disposed between the pair of hydronic tubes 24′, as shown in FIG. 4B. The first and second manifolds 54′, 56′ can then be attached to the respective first and second end portions 41′, 42′ of the pair of hydronic tubes 24′ so that the first manifold 54′ is connected both first end portions 41′ of the pair of hydronic tubes 24′ and the second manifold 56′ is attached to both second end portions 42′ of the pair of hydronic tubes 24′. Alternatively, the end portions can be configured as shown in FIG. 4A. In this case, the attachment of the manifolds to the end portions is identical to that disclosed for the heat exchanger 20 except that one of the hydronic tubes 24′ of the pair of hydronic tubes 24′ will be attached to third and fourth manifolds 78′, 80′. The end portions 26′, 28′ of the process tube 22′ and the end portions 41′, 42′ of the pair of hydronic tubes 24′ can then diverge in a variety of manners to form the heat exchanger shown in FIG. 4A. The heat exchanger 20′ can then be shaped into a desired configuration.

[0047] Finally, to form the heat exchanger shown in FIGS. 7-9D, each process tube 22″ is disposed between a pair of hydronic tubes 24″. The process tubes 22″ and hydronic tubes 24″ are arranged so that they alternate in a configuration, such as that shown in FIG. 7, with there preferably being one more hydronic tube 24″ then there is process tubes 22″. The intermediate portions 30″, 44″ are arranged so that they abut one another and portions of the heat transfer surfaces 32″, 34″ of each process tube 22″ is in a heat conducting contact with portions of the heat transfer surfaces 46″, 48″ of the hydronic tubes 24″. The manifolds 37″, 38″ can then be attached to the end portions 26″, 28″ of the process tube 22″ as was discussed previously. The manifolds 54″, 56″, 78″, 80″ can also be attached to the end portions 41″, 42″ of the hydronic tubes 24″ as was discussed above. The heat exchanger 20″ can then be shaped into a desired configuration depending upon the application in which the heat exchanger 20″ is to be used.

[0048] The above-described heat exchangers 20, 20′, 20″ made according to the principles of the present invention have an increased heat transfer efficiency due to the increased heat transfer that can occur between a process fluid and a hydronic fluid. The increased efficiency enables the heat exchangers 20, 20′, 20″ to be smaller in size for a given application. A smaller size can enable a reduction in size of the equipment within which the heat exchanger 20, 20′, 20″ is used. The increased efficiency can also reduce the cost of the heat exchanger 20, 20′, 20″.

[0049] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

What is claimed is:
 1. A flattened tube heat exchanger, the heat exchanger comprising: a first and second flattened tube each having first and second ends with an intermediate portion therebetween and opposite heat transfer surfaces that extend between said first and second ends, said first tube having a plurality of hydraulically discrete internal passageways that extend through said first tube between said first and second ends of said first tube and allows a fluid to pass therethrough, said second tube having at least one internal passageway that extends through said second tube between said first and second ends of said second tube and allows a fluid to pass therethrough, and said second tube being disposed adjacent said first tube with said intermediate portions abutting and portions of said heat transfer surfaces that extend along said intermediate portions being in heat conducting contact; and first and second pairs of manifolds, said first pair being attached to and in fluid communication with said first and second ends of said first tube so that a fluid can pass between said first pair via said plurality of passageways in said first tube, and said second pair being attached to and in fluid communication with said first and second ends of said second tube so that a fluid can pass between said second pair via said at least one passageway in said second tube.
 2. The heat exchanger of claim 1, wherein: said at least one passageway is one of a plurality of passageways in said second tube with each passageway in said second tube being hydraulically discrete.
 3. The heat exchanger of claim 2, wherein: said passageways in said first and second tubes each have a hydraulic diameter of less than 2.5 millimeters.
 4. The heat exchanger of claim 1, wherein: said passageways in said first tube each have a hydraulic diameter of less than 2.5 millimeters.
 5. The heat exchanger of claim 4, wherein: said passageways in said first tube each have a hydraulic diameter of less than approximately 2.0 millimeters.
 6. The heat exchanger of claim 5, wherein: said passageways in said first tube each have a hydraulic diameter of less than approximately 1.5 millimeters.
 7. The heat exchanger of claim 1, wherein: said intermediate portions extend sinuously between said first and second ends.
 8. The heat exchanger of claim 1, wherein: said intermediate portions are coiled.
 9. The heat exchanger of claim 1, wherein: said intermediate portions are generally straight.
 10. The heat exchanger of claim 1, wherein: said intermediate portions have a single 90 degree bend and are generally L-shaped.
 11. The heat exchanger of claim 1, wherein: said intermediate portions have two 90 degree bends and are generally U-shaped.
 12. The heat exchanger of claim 1, wherein: said abutting intermediate portions are brazed together.
 13. The heat exchanger of claim 1, wherein: said ends extend into slots in said manifolds.
 14. A flattened tube heat exchanger, the heat exchanger comprising: a first, second, and third flattened tube each having first and second ends with an intermediate portion therebetween and opposite heat transfer surfaces that extend between said first and second ends, said first tube being disposed between said second and third tubes with said intermediate portions abutting and portions of said heat transfer surfaces that extend along said intermediate portions being in heat conducting contact, said first tube having a plurality of hydraulically discrete internal passageways that extend through said first tube between said first and second ends of said first tube and allow a fluid to pass therethrough, said second and third tubes each having at least one internal passageway that extends through said second and third tubes between said first and second ends of said second and third tubes and allows a fluid to pass therethrough; and a plurality of manifolds, each manifold being attached to and in fluid communication with at least one end of said first and second ends.
 15. The heat exchanger of claim 14, wherein: said plurality of manifolds are first and second pairs of manifolds, each manifold of said first pair being attached to and in fluid communication with different ends of said first tube and being disposed between said second and third tubes, and each manifold of said second pair being attached to different ends of said second tube and to different ends of said third tube.
 16. The heat exchanger of claim 14, wherein: said at least one passageway in each of said second and third tubes is one of a plurality of passageways and each passageway in each of said second and third tubes is hydraulically discrete.
 17. The heat exchanger of claim 16, wherein: each passageway in each of said tubes has a hydraulic diameter of less than 2.5 millimeters.
 18. The heat exchanger of claim 14, wherein: each passageway in said first tube has a hydraulic diameter of less than 2.5 millimeters.
 19. The heat exchanger of claim 18, wherein: each passageway in said first tube has a hydraulic diameter of less than approximately 2.0 millimeters.
 20. The heat exchanger of claim 19, wherein: each passageway in said first tube has a hydraulic diameter of less than approximately 1.5 millimeters.
 21. The heat exchanger of claim 14, wherein: said ends of said tubes diverge as said ends extend from said intermediate portions.
 22. A flattened tube heat exchanger, the heat exchanger comprising: a plurality of first and second tubes each having first and second ends with an intermediate portion therebetween and opposite heat transfer surfaces that extend between said first and second ends, said first tubes each having a plurality of hydraulically discrete internal passageways that extend through said first tubes between said first and second ends of said first tubes and allow a fluid to pass therethrough, said second tubes each having at least one internal passageway that extends through said second tubes between said first and second ends of said second tubes and allows a fluid to pass therethrough, and each of said first tubes being disposed between two second tubes with said intermediate portions abutting and portions of said heat transfer surfaces that extend along said intermediate portions being in heat conducting contact; and a plurality of manifolds, each manifold being attached to and in fluid communication with at least one end of said first and second ends.
 23. The heat exchanger of claim 22, wherein: said plurality of manifolds are a plurality of first and second pairs of manifolds, each manifold of said first pairs, being attached to different ends of said first tubes and being disposed between said second tubes, and each manifold of said second pairs being attached to an end of at least one second tube of said plurality of second tubes.
 24. The heat exchanger of claim 22, wherein: said at least one passageway in each second tube of said plurality of second tubes is one of a plurality of hydraulically discrete passageways.
 25. The heat exchanger of claim 24, wherein: each passageway in each of said plurality of first and second tubes has a hydraulic diameter of less than 2.5 millimeters.
 26. The heat exchanger of claim 22, wherein: each passageway in said plurality of first tubes has a hydraulic diameter of less than 2.5 millimeters.
 27. The heat exchanger of claim 26, wherein: each passageway in said plurality of first tubes has a hydraulic diameter of less than approximately 2.0 millimeters.
 28. The heat exchanger of claim 27, wherein: each passageway in said plurality of first tubes has a hydraulic diameter of less than approximately 1.5 millimeters.
 29. A method of making a flattened tube heat exchanger, the method comprising the steps of: attaching an intermediate portion of a first flattened tube to an intermediate portion of a second flattened tube so that said intermediate portions are abutting and portions of heat transfer surfaces on said first and second tubes are in heat conductive contact; attaching a first pair of manifolds to ends of said first tube so that each manifold of said first pair is attached to different ends of said first tube; attaching a second pair of manifolds to ends of said second tube so that each manifold of said second pair is attached to different ends of said second tube; and shaping said attached tubes into a predetermined configuration.
 30. The method of claim 29, wherein: said first tube has a plurality of hydraulically discrete internal passageways that each have a hydraulic diameter of less than 2.5 millimeters and extend through said first tube between said ends of said first tube so that a fluid can pass therethrough.
 31. The method of claim 29, wherein the step of attaching an intermediate portion of a first tube includes: disposing said first tube between a pair of second tubes with said intermediate portion of said first tube abutting intermediate portions of said second tubes and portions of heat transfer surfaces on said intermediate portion of said first tube being in heat conducting contact with portions of heat transfer surfaces on said intermediate portions of said pair of second tubes.
 32. The method of claim 31, wherein: the step of attaching a first pair of manifolds includes disposing said first pair of manifolds between said pair of second tubes; and the step of attaching a second pair of manifolds includes attaching each manifold of said second pair of manifolds to both tubes of said pair of second tubes so that each manifold of said second pair of manifolds is attached to different ends of each tube of said pair of second tubes.
 33. The method of claim 29, wherein: the step of attaching an intermediate portion of a first tube includes disposing each first tube of a plurality of first tubes between two second tubes of a plurality of second tubes with intermediate portions of each tube abutting adjacent intermediate portions and portions of heat transfer surfaces on said intermediate portions of each tube being in heat conducting contact with adjacent portions of heat transfer surfaces on said adjacent intermediate portions; the step of attaching a first pair of manifolds includes attaching a plurality of first pairs of manifolds to ends of said first tubes so that each first pair is attached to different ends of a single first tube; and the step of attaching a second pair of manifolds includes attaching a plurality of second pairs of manifolds to ends of said second tubes so that each second pair is attached to different ends of at least one second tube of said plurality of second tubes.
 34. The method of claim 29, wherein the step of shaping said attached tubes includes: shaping said attached tubes so that said intermediate portions extend sinuously between said ends of said tubes.
 35. The method of claim 29, wherein the step of shaping said attached tubes includes: shaping said attached tubes so that said intermediate portions are coiled.
 36. The method of claim 29, wherein: the step of attaching said intermediate portions includes brazing said abutting intermediate portions; the step of attaching a first pair of manifolds includes brazing said first pair of manifolds to said ends of said first tube; and the step of attaching a second pair of manifolds includes brazing said second pair of manifolds to said ends of said second tube. 